Document DGV5VoGorORmxppvbJpNqZa4o

.RVARD UNIVERSITY ' School of Public Health 55 Van Dyke St Boston, Mass.. March 10, 1925 Dear Gal: 1 Referring to my letter of yesterday and the auestion of air motion within the cabinet, please remember that the cabi net volume is about 75,000 liters and that we arc not samp ling continuously. Some convection currents are inevitable from temperature difference effects and the withdrawal of 30 to 150 liters at various times. Then air is withdrawn.it is replaced through a mask impenetrable to the fume particles. Air flows through the Tyndallmeter at about 20 liters ;p'er"min." r, > and;-is blown back again-into-the cabinet. It is--true ithat " -v * " ' Tolmah and, Vliet found this promoted flocculation of the fume -- o particles Rand we have found this to be the case, but their cabiriet was,' I think, very small. V/e have to run several fans ^ -to .get the same result. ^ <_ I do not herald our curves as anything new or unexpected A and hope you did-not get this idea. They represent still air j conditions or come as near to it us you can. Y/e cannot run the precipitator inside the cabinet nor discharge the air es- / caping from it into the cabinet, as it is too highly ionised and of itself effects flocculation. If you want to read the Tyndallmeter inside the cabinet you are welcome to the job - personally I don't because you would have to;wear a mask the entire time - 24 hours. Observers cannot keep going in. .and ' out as fume always escapes which spoils the continuity of the experiments. - ' As a matter of fact I think these curves support the Bu* . reau of Mines report rather than contradict it. They show some reason for the high percentage of particles exhaled in ' their breating experiments. He got comparable results in gas masks - the Pb3r2 fume passed through fairly easily and would not plug the mask - flocculating substances like "nO plug masks rapidly and rapidly make them very efficient filters. I wrote Mr. Yant at the Bureau of Mines and sent him the curves. I am going to send him slides of the fumes for microscopic study - something which they have apparently ig nored up to the present although fully aware of its signifi cance in the quantity inhaled and retained. Rieldner and Sayers have already seen some of mine. Sincerely yours Philip Drinker (signed)